Positive identification of a magnon sideband in KNiF3 through magnetic circular dichroism

The MCD of the 1E region of KNiF3 unambiguously identifies the prominent satellite at 16154 cm−1 as a magnon sideband. By consideration of the site group symmetries this can be shown to be associated with a Γ3+ exciton pair. The unusually large separation from the origin leads us to identify the band as due to a combined magnon-phonon-exciton process.